Dynamic analysis of different levels of constraint in Total Knee Arthroplasty during Gait and Squat: a Finite Element study

Total Knee Arthroplasty (TKA) is a successful orthopaedic surgical procedure performed to restore physiological functionality in pathological knee, but implant failures and patient dissatisfaction during activities still persist. Several TKA implants with different levels of constraint are currently available on the orthopaedic market, and just some of them have been compared to evaluate how each design can affect the knee biomechanics during dynamic activities. Thus, a more comprehensive biomechanical study among them could be helpful for the surgeon to better understand TKA performance thus facilitating the decision-making process and also to meet the necessity of a more scientific rationale for post-TKA activities. Basing on a previously validated knee model, the purpose of this study is to compare the knee biomechanics effect due to five common prosthetic implants (Mobile Bearing (MB) Cruciate Retain (CR) and Ultra-Congruent (UC), Fixed Bearing (FB) CR, Posterior Stabilized (PS) and Condylar Constrained Knee (CCK)) characterized by different levels of constraint, simulating gait and squat. By means of Finite Element Analysis (FEA), these designs have been incorporated in the virtual model of the lower leg, with patellar component and patellar tendon included, and consequently analysed in terms of polyethylene stress and tibial bone stress, tibiofemoral and patellofemoral kinematics, and kinetics. The outcomes have been compared among the models, showing that UC design shows the best kinematics and kinetics performance with respect to the other implants, and that TF contact stress changes with the difference in design constraint. Congruency and mobility are design factors that can rise the insert stress, while the addition of constraint in CCK reduces the stress with respect to PS, which moreover generated the highest stress values. Thus, the higher the constraint level, the lower the stress on the insert. It has been observed that through the squat simulation it is possible to offer a better overview of the TKA performance with respect to gait. Future developments could integrate this analysis considering other designs, modelling patient-specific variations and simulating other activities.